Acquired immunodeficiency syndrome (AIDS) is the result of infection by the retrovirus known as human immunodeficiency virus (HIV). It remains a major medical problem, with an estimated 35 million people infected worldwide at the end of 2013. During that year, there were 2.1 million new infections, with 1.5 million people dying from complications due to AIDS.
Current therapy for HIV-infected individuals consists of a combination of approved anti-retroviral agents. Over two dozen drugs are currently approved for HIV infection, either as single agents, fixed dose combinations or single tablet regimens, the latter two containing 2-4 approved agents. These agents belong to a number of different classes, targeting either a viral enzyme or the function of a viral protein during the virus life cycle. Thus, agents are classified as either nucleotide reverse transcriptase inhibitors (NRTIs), non-nucleotide reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), integrase inhibitors (INIs), or entry inhibitors (one entry inhibitor, maraviroc, targets the host CCR5 protein, while the other, enfuvirtide, is a peptide that targets the gp41 region of the viral gp160 protein). In addition, a pharmacokinetic enhancer with no antiviral activity (cobicistat) has been approved for use in combinations with antiretroviral agents (ARVs) that require boosting.
Despite the armamentarium of agents and drug combinations, there remains a medical need for new anti-retroviral agents, due in part to the need for chronic dosing to combat infection. Significant problems related to long-term toxicities are documented, creating a need to address and prevent these co-morbidities (e.g., CNS, CV/metabolic, renal disease). Also, increasing failure rates on current therapies continue to be a problem, due either to the presence or emergence of resistant strains or to non-compliance attributed to drug holidays or adverse side effects. For example, despite therapy, it has been estimated that 63% of subjects receiving combination therapy remained viremic, as they had viral loads >500 copies/ml (Oette, M. et al., “Primary HIV Drug Resistance and Efficacy of First-Line Antiretroviral Therapy Guided by Resistance Testing”, J. Acq. Imm. Def. Synd., 41(5):573-581 (2006)). Among these patients, 76% had viruses that were resistant to one or more classes of antiretroviral agents. As a result, new drugs are needed that are more convenient, have high genetic barriers to the development of resistance and have improved safety over current agents.
It is now well known that cells can be infected by HIV through a process by which fusion occurs between the cellular membrane and the viral membrane. The generally accepted model of this process is that the viral envelope glycoprotein complex (gp120/gp41) interacts with cell surface receptors on the membranes of the target cells. Following binding of gp120 to cellular receptors (e.g., CD4 in combination with a chemokine co-receptor such as CCR5 or CXCR4), a conformational change is induced in the gp120/gp41 complex that allows gp41 to insert into the membrane of the target cell and mediate membrane fusion. As these entry processes occur on the cell membrane, they are amenable for inhibition by macrocmolecules, which include biologic peptides (Haqqani et al., Antiviral Res., 98:158 (2013)). For instance, the approved antiviral peptide enfuvirtide (FUZEON®) targets a region of gp41 involved in membrane fusion. Larger polypeptides such as monoclonal antibodies can also inhibit different aspects of virus entry. A monoclonal antibody targeting the first step of virus entry, interaction with the cellular receptor CD4 (ibalizumab; Bruno et al., J. Antimicrob. Chemother., 65:1839 (2010)), as well as a monoclonal antibody targeting the co-receptor CCR5 (PRO-140; Tenorio, Curr. HIV/AIDS Rep., 8:1 (2011)) have both shown positive results in Phase 2a trials. These antibodies also have the property of being long acting antiretrovirals, with potential dosing regimens of weekly to monthly (Jacobson et al., J. Infect. Dis., 201:1481 (2010); Jacobson et al., Antimicrob. Agents Chemother., 53:450 (2009)).
Another property of peptide entry inhibitors is that enhanced or synergistic potency can be obtained if two peptide inhibitors are attached to each other, or if a single inhibitor is localized near the site of action through binding to membrane biomolecules. Thus, attaching a fusion peptide inhibitor to a monoclonal antibody targeting CCR5 (Kopetzki et al., Virol. J., 5:56 (2008)) or attaching a cholesterol moiety to the C-terminus of a peptide fusion inhibitor to place it at the surface of the target cell membrane (Ingallinela et al., Proc. Natl. Acad. Sci. USA, 106:5801 (2009); Augusto et al., J. Antimicrob. Chemother., 69:1286 (2014)) drastically increases the potency of the combined molecule compared to the separate molecules. Similarly, bispecific antibodies consisting of anti-HIV-1 neutralizing antibody fragments targeting gp120 fused to ibalizumab showed synergistic increases in potency compared to the individual inhibitors (Sun et al., J. Acquir. Immune Defic. Syndr., 66:473 (2014)). The Combinectin molecules of the invention makes use of these various properties.